The week before a Banksy sculpture went on display in the Walker Art Gallery in Liverpool. It was the vandalised bust of a priest, his face sawn off and replaced with tiles to give a pixellated effect. Called Cardinal Sin, the sculpture commented on the alleged child abuse cover-up in the Catholic church. Cardinal Sin is on indefinite loan to the gallery. The only condition for its display was that the sculpture was placed alongside the 17th-century religious works.

Banksy also put out a statement, saying: “I love everything about the Walker Gallery – the Old Masters, the contemporary art, the rude girl in the café. And when I found out Mr Walker built it with beer money, it became my favourite gallery.”

Apparently that is the voice of the underground speaking. Hardly radical, is it? Taking popularist pot-shots from the heart of an institution. For a man who has made his career out of puncturing capitalism and mocking the establishment, this is not the most revolutionary of creeds.

But then Banksy is not a radical. He just pretends to be.

Banksy’s art is aimed at affluent people with a soft spot for anarchism. The kind of people who live in bubbles, untroubled by ugly compromises like markets and democracy. Cultured, but a bit thick. Concerned, but ultimately nihilistic.

And Banksy has exploited his underground status to launch an incredibly mainstream artistic career. He can now boast all the usual trappings of success: sell-out exhibitions, celebrity fans, and an Oscar-nominated film. But it was during the run-up to this year’s Oscars, when Exit Through the Giftshop had been nominated for best documentary, and Banksy's work started popping up all over Los Angeles, that it became clear what a con it all was. Banksy’s grafitti isn’t art, it’s just a skilfully disguised advert.

These days if there is a Banksy on a wall near you, the chances are your council will have done everything in their power to keep it. Rather than paying someone to have the graffiti removed, local authorities will be petitioning to protect it for adding vibrancy, as well as value, to the neighbourhood.

Guy Debord, founder of the Situationist movement, had a word for this: recuperation. Recuperation is the process by which the establishment commodifies a radical image or idea, and so robs it of any subversive power. Like Che Guevara posters on student walls, or existentialist philosophy on bumper stickers.

Debord blamed recuperation on the capitalist system. Graffiti fans would probably blame local government. But really there is only one person who is responsible. And that's Banksy.